This review describes advantages and limitations of registries that base their analyses on the census of all patients. Registries may utilize the random sample approach to enrich their data for more detailed and informative research. The Dialysis Outcomes and Practice Pattern Study (DOPPS) and its random sample approach is discussed here in detail, with examples on the value of this method. The DOPPS is currently being expanded to allow for even more valuable studies. This methodology can also be applied to large countries that do not have an existing registry, as it is an effective way of collecting detailed information at a relatively low cost that is representative of the country or population as a whole.